Hot water delivery problem with tempering valve and recirc loop

[Kevin Dierkes]

Apologies in advance for a long post. Want to be thorough here to be sure all needed information is included.

Have an issue that is challenging my normally solid troubleshooting skills. Setup is a restaurant space with hot water run direct from heater to dishwashing sinks and equipment, and all other fixtures (hand sinks, bathrooms, etc.) fed via a Symmons 7-400 thermostatic mixing valve, and there is a hot water recirc loop present. Connections for all this are done to the diagram (diagram #2) shown in the Symmons install manual for the 7-400, with all specified one way checks and ball valves present. Only suggested item not present is a second thermometer on the recirc return line. Cold supply pressure is set via PRV at 75 lbs, and an inline gauge indicates this is holding steady.

This install was done by others, I was contacted to address a lack of hot water pressure and temperature. This is an existing space about 40 years old, and has been refitted numerous times for different restaurant tenants, resulting in a patchwork of abandoned and rerouted lines that confuse the issue and make tracing difficult

Initial customer complaint was almost no hot pressure anywhere but at dishwashing station. Tempering valve was badly scaled up, disassembled and cleaned, reassembled with new factory case seal and sleeve o-ring kit. Full pressure was thus restored to all affected fixtures. However, water runs hot for only 10-15 seconds at any fixture then falls back to cool - less than lukewarm, but slightly warmer than the cold supply - and remains that way unless the faucet is turned off and some time allowed to pass before opening the hot again, in which case the process repeats.

Thermometer on outgoing line from the 7-400 holds generally steady at 110° as was previously set, and that (outgoing tempered hot) line is hot to the touch. The recirc pump has power and is running (sounds normal, have not verified impeller is intact as yet) but the return line at the ingoing side of the recirc pump is cool to the touch, essentially ambient room temperature, as though there is no flow.

The recirc line ties back into the cold supply to the heater and mixing valve past an inline check valve and a ball valve that was placed (per suggested installation diagram) to "fine tune" the amount of water from the return being fed back to the 7-400. I suspect this ball valve may be bad, as it turns a full 90° stop to stop but doesn't feel right, as though it was internally scaled up and forced at some point damaging the seal.

The short explanation of the current problem is that after an initial 10-15 seconds of decent hot water at any fixture fed from the mixing valve, it drops off to just barely warmer than the cold water, as though there is cold water being back fed into the hot side after the mixing valve, and the return never gets hot or even warm to the touch. Pressure to the fixtures remains constant (and good, equal to cold pressure) irrespective of the temperature.

Disassembly is a challenge here due to a tight installation and very close proximity to several electrical load centers, making it a concern to have any water spraying in the vicinity. Any suggestions on whether I should suspect a bad recirc pump/volute blockage, or something else entirely.

I'd add all water lines are run above the ceiling, so the recirc line should theoretically operate at least partly by gravity even if the pump is inoperative, barring a full blockage. I've also considered there may be an inline valve on the recirc line hidden somewhere above the drop ceiling that is closed for reasons not known to me. If that is the case, I'll be spending a lot of time on a ladder popping ceiling tiles trying to find it. It is acting like there is a cross connect present, but so far I've not located any specific fixture or piece of equipment that would be causing that.

Hoping someone here will have encountered a similar problem and can make a suggestion that will reduce the diagnostic time required and avoid a wild goose chase. Appreciate any and all input.

 

[James Henry]

I had a similar situation recently and found that a ghost had shut a valve off on the recirculating line. that ball valve might be broken shut.
open it and then close it and test the system in both positions.

 

[Sponsor]

 

[Kevin Dierkes]

James, thanks for your advice. In the situation you encountered did the recirc loop being closed off result in poor or no hot water at the hot side of any or all fixtures? Because that is essentially what I'm encountering here, save for a brief burst of hot when a faucet is first opened after some period of no water being run. It acts almost like a cross connect from the cold to hot supply lines.

Should probably point out that the thermometer that monitors the outgoing water temp consistently reads close to 110°F as set on the mixing valve, but that water isn't making it to downstream sinks. So, the temperature at point of use does not reflect the shown water temperature. And the copper line leaving the tempering valve is hot to the touch as far as I can see and feel it until it goes above the ceiling.

I'd expect with the recirc loop not working, I'd still get hot water but would take time to run out the water that was "in line" between the heater and the downstream fixture first. Running any of the sinks, even those physically closest to the heater and tempering valve for 10+minutes results in never getting anything more than barely lukewarm water, save for the initial burst of hot that comes out when first turned on.

 

[Jadnashua]

IF there are any valves, a spray is a common one, where you adjust the water with two valves, and then use the lever on the sprayer to turn the water on/off, that can create a cross-over, meaning the hot and cold get mixed beyond that. The water will take the path of least resistance. That can vary by the length of the pipes, the elevation, the sizes, and the number of elbows along the path, so it can be sometimes a bit misleading.

If there are shutoffs for any of the valves, try turning the cold off one by one while trying to see if that makes any difference in the performance on the other outlets. If there is a sprayer and you want to leave it like it is, add a check valve on the hot side so the cold can't cross-0ver. Conversely, if there are cold outlets that are always warm, you may need a check valve on the cold side as well. Because of the water heater, that path usually has more resistance or friction on the flow, so the cold tends to overcome it a bit more often.

If you have any automatic faucets in say lavatories that have preset temperature, one of those may have a worn out check valve.

 

[Plumber01]

The recirc line ties back into the cold supply to the heater and mixing valve past an inline check valve and a ball valve that was placed (per suggested installation diagram) to "fine tune" the amount of water from the return being fed back to the 7-400. I suspect this ball valve may be bad, as it turns a full 90° stop to stop but doesn't feel right, as though it was internally scaled up and forced at some point damaging the seal.

The ball valve should act as a balancing valve regulating water back to the heater not the mixing valve. From your description I quoted, I cant tell if you're saying the ball valve is on the line going to the mixing valve or the heater. You said its piped exactly like the installation instructions which is the correct way to do it.

In my experience, the ball valve, or balancing valve, should be set anywhere between 5-20% open, returning most of the water to the mixing valve, not the heater. The majority of the water needs to circulate through the mixing valve during periods of no draw.

If piped correctly, I would suspect the ball valve (balancing valve) is shot or not adjusted correctly.

 

[Kevin Dierkes]

Ok, some further thoughts. I'll be headed back to this job Saturday AM, but there is in fact a T&S pre-rinse station that could be a cross connect point. No automatic faucets (I'd looked for those as a likely candidate right away). Everything but the lav faucets are two handle Chicago or T&S in the kitchen and bar areas. Mop sink is a two handle Chicago, integral vacuum breaker has already been verified to be working properly.

The inline check valves used on the piping involved in the recirc loop and mixing valve are all spring check type, not swing checks, which I prefer for reliability and ease of service. I've never been a fan of spring checks as they are easily fouled with scale, especially in hot water applications. So, those are suspect as well.

I think my structured troubleshooting approach is going to be as follows:

1. Close off cold control stops (and hope they work, heh) to any fixtures that could create a cross connect. The only things I've noted so far are the T&S pre rinse, and a few single handle lav faucets (manually operated).

2. If step 1 doesn't provide a positive fix (if it does, checks will be added as needed) then pull the recirc pump motor and let the return line dump to to floor drain to see if I get hot water coming back. If I get no flow form there, then there has to be a valve somewhere up line closed off, the loop was cut and capped off at some point in a previous remodel, or the line is scaled shut.

3. If I do get flow of hot water from return line in step 2, then suspect a bad inline spring check, or a bad ball valve screwing up the temp mix. If I get flow but it is cold water, then circle back to step one in assuming a cross connect exists somewhere in the system.

Any obvious things I'm not listing there that I should also be checking? Much thanks for the helpful input so far.

 

[Reach4]

Temperature can be another clue. An unused faucet should have its supply pipes at ambient. You may be able to identify the temperature by touch, or maybe a cheap non-contact infrared temperature gun would be good. Water crossing over would be a different temperature.

There are some really nice, reasonably priced FLIR cameras for Android and IOS. https://www.flir.com/products/flir-one-gen-3/ I would suggest that would have a lot of applications for you.

 

[Tuttles Revenge]

T&S faucet have created crossover at one of my restaurant clients.. I think we installed cartridges that have check valves built in.. Was probably a decade ago so fuzzy memory..

 

[Kevin Dierkes]

Good point on the temperature of the lines being a clue. I have a standalone non-contact digital thermometer, will take that along. Access to the lines under the bathroom sinks is difficult as there is a baffle mounted to conceal the traps and supply lines, I'll have to remove that to see or touch anything in the two main restrooms.

There is a one-holer employee restroom with a wall hung lav with typical ADA rubber guards on the trap and the supply lines/stops. The restrooms all have single handle lav faucets of similar type installed. Aside from these, the T&S pre rinse is the only other fixture I've identified as a possible cross-connect source.

There are two dishwashers (Ecolab in bar for glasswares) and a larger one in kitchen that are hot water supply only, so those can be eliminated from consideration. Hand sinks and 3 compartment sinks in kitchen and at bar are all two handle faucets.

I'm leaning towards a cross connect being the issue since even if there was no flow on the recirc line, I don't see that screwing up the hot water getting to each fixture, just that there will be a delay in it getting up to temperature. The only caveat to that is if the ball valve or check valve on the recirc line that is feeding back to the water heater inlet and the cold inlet on the tempering valve are bad, it could be back feeding cold water into the hot side of the system the way this is configured. The fact that the outgoing line from the tempering valve is hot to the touch contradicts that possibility, however.

Will post back with results and resolution as soon as I have this mess fixed.

 

[Tuttles Revenge]

I've used my FLIR add on camera for my android phone a LOT for this sort of diagnosis. This one to trace the ceiling radiant heat system for demo work and re-routing of lines.

 

[James Henry]

If you think about it, you said that you get a burst of hot water from the faucets then it turns cold. That's a tell tale sign of a cross-over. When the pressure drops in the hot water line because a faucet opens, the higher cold water line pressure moves to replace it. When that would happen to me the first place I would look is the mop sink. if their is a hose hooked up to the mop sink faucet and the hose has a shut off valve on it, custodians will just use the shut off valve on the hose and not shut the hot and cold faucets off because it is easier. PRESTO!, Cross connection. Check that.
We're all limited with are ability to help because we're not there. Good luck.

 

[Kevin Dierkes]

There is a combined "Y" hose on the mop sink, one of the first things I eliminated as I made certain the faucet was off, both hot and cold.

In another strange twist, there is now proper hot water to all fixtures previously affected by lack of same, without my doing anything further. So, there is an intermittent problem - probably a cross connect - and as of today it is not present.

Clearly, I can't diagnose without the symptom present so will need to wait for the hot water delivery problem to reoccur before I can go back over there and have a another stab at it. I hate intermittent stuff like this, because it not only makes it difficult to give a firm answer for the cause and a definite repair, but because from the customer's perspective it makes me look like a doofus.

Further updates will be posted if I ever get a chance to nail this thing down positively. Again, I appreciate all efforts to assist to this point, and hope I'll be able to report back with a final determination so this isn't left open ended.

 

[Kevin Dierkes]

Ok, an update on this. Went back this morning after customer reported poor hot water pressure again. Temperature has been good most of the last week, oddly enough, but now the hot water pressure is marginal again - 25 to 30 lbs - at all fixtures served by the tempering valve. I verified no valves in the mechanical room had been tampered with from my previous trip, and disassembled the tempering valve to verify the spool was rotating freely, which checked good.

I can watch the inline temperature and pressure gauge on the outgoing line from the tempering valve drop from 65-70 lbs static pressure down to 25-30 as soon as a faucet or the bar dishwasher places demand on the line. For a further wrinkle, I found two Watts CSM61-M1 balancing valves on the two ends of the return loop before they are teed back together ahead of the recirc pump. These were hidden above the drop ceiling in the mechanical room and not readily visible without some contorted poking around on a ladder. Poor placement for sure but then generally shouldn't need adjustment once balanced.

As of now I can't shake the inclination I have more than one problem in play. Presently both the pressure and the temperature on the hot at all fixtures down stream from the tempering valve are low, I am attributing the temperature problem to an intermittent cross connect that I still need to track down. However, the pressure issue could be due a bad ball valve not fully open (even though all visible valves appear to be fully open by handle position), or a bad inline spring check valve that is crusted shut or otherwise hung up.

I don't suspect a line scaled shut causing the low pressure as the pressure drop was sudden, just recurred yesterday. Main cold line water pressure is regulated at 70 lbs and is reading steady via the gauge on the main line just downstream from the PRV.

My next plan of attack is to get here well ahead of normal opening time Monday, shut off the main water and start verifying the function of ball valves, checks and the recirc loop. I suspect there is a problem on the recirc loop since the return line temperature is barely above the cold supply line, this was measured with an IR thermometer.

Temperature of the supply water via the tempering valve is 110°F, and there is no way the return water is coming back that cold unless a cross connect is putting cold water in the line somewhere upstream of the pump. I'm also now left with the possibility there is a problem with one or both of the hidden flow control valves above the ceiling affecting the proper operation of the recirc loop.

If anyone thinks I'm off base here, or has a suggestion for something I may have overlooked, have at it. This one has me stymied right now, and anything I can do to expedite the troubleshooting and remediation of this mess would be great. I had the pressure problem corrected last week after servicing the tempering valve - which was seized up with scale - though the intermittent temperature drop issue remained. Now I'm back to square one, which is doubly frustrating.

 

[Reach4]

Very unlikely to identify the problem, but easy to check: I would put a pressure gauge on the WH drain valve to test that the water is not being slowed on the way into the WH.

Of course if the dishwashing sinks are known to not have a flow problem, the flow into the WH is not the problem.

 

[James Henry]

Open a faucet and tap on the check valves one at a time and check the water flow as you go. You definitely have a constriction problem. Any galvanized pipe in there.